Doctors treating the 24 U.S. diplomats and their spouses who mysteriously fell ill in Cuba in 2016 after an attack on U.S. Embassy in the country, say brain abnormalities have been found in the patients.

According to a new report, white matter which allows different areas of the brain to communicate found in the embassy workers had “developed changes”.

Some victims knew immediately that the attack was affecting their bodies, while some developed physical symptoms within 24 hours.

Other Americans who were not working but were traveling in Cuba had also reported experiencing weird symptoms similar to those that the U.S. officials reported, the State Department said.

While investigators had initially suspected what personnel were expecting as “sonic attacks,” officials are now avoiding that term.

Secretary of State Rex Tillerson said Tuesday that he believes the Embassy workers were victims of “targeted attacks,” but noted the U.S. doesn’t know who perpetrated them.

However, Tillerson did say that the blame for the attacks falls on Cuba, as its government is responsible for the safety of diplomats in their country.

Cuba has denied all accusations of involvement and claimed the Trump administration was “deliberately lying” about the attacks.

The Cuban government has also asked that the U.S. to release its findings of the attacks for Cuba to investigate.

Tillerson has said that while the U.S. had released some information, the country won’t release additional details that could allow the perpetrator to determine how effective the attacks were.

Most of the victims have fully recovered, but some still have persistent symptoms.

The last of the mysterious attacks in Cuba was reported in August, but the State Department is requiring its employees going to Cuba to undergo various tests, as it hasn’t ruled out the possibility of future mystery attacks.